This invention relates in general to valves for controlling fluid flow and more particularly, to a fluid flow control assembly for controlling flow of a fluid, such as a refrigerant, in a first direction of flow, and permitting substantially unrestricted flow of the fluid in a second direction of flow.
Valves are widely used for controlling the flow of a fluid from a source of pressurized fluid to a load device or from a load device to a low-pressure reservoir. Frequently, a pump, a compressor, or other pressure-increasing device, is provided as the source of pressured fluid, typically operating to draw low-pressure fluid from the reservoir, mechanically acting on the fluid to increase the pressure of the fluid, and discharging the pressurized fluid. The flow of the fluid discharged from the pressure-increasing device is typically selectively controlled by a valve to control the operation of the load device.
One type of valve is a microvalve. A microvalve system is a MicroElectroMechanical System (MEMS) relating in general to semiconductor electromechanical devices.
MEMS are a class of systems that are physically small, having features or clearances with sizes in the micrometer range or smaller (i.e., smaller than about 10 microns). A MEMS device is a device that at least in part forms part of such a system. These systems have both electrical and mechanical components. The term “micromachining” is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices.
MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today there are many more micromachining techniques and materials available.
The term “MEMS device” as may be used in this application means a device that includes a micromachined component having features or clearances with sizes in the micrometer range, or smaller (i.e., smaller than about 10 microns). It should be noted that if components other than the micromachined component are included in the MEMS device, these other components may be micromachined components or standard sized (i.e., larger) components (also referred to as “macro-sized components”). Similarly, the term “microvalve” as may be used in this application means a valve having features or clearances with sizes in the micrometer range, or smaller (i.e., smaller than about 10 microns) and thus by definition is at least partially formed by micro machining. The term “microvalve device” as may be used in this application means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or macro-sized components (i.e., components larger than micromachined components).
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or control element movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the control element blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the control element moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
One type of microvalve device is a direct acting microvalve that consists of a beam resiliently supported at one end in a housing to control the flow of a fluid between ports formed in the housing. In operation, an actuator forces the beam to bend about the supported end of the beam. As the beam bends, the ports in the microvalve housing are uncovered or covered (that is, progressively opened or closed) to control fluid flow through the ports, and thus through the microvalve. Such a direct acting microvalve may be used as a pilot valve to control the operation of a main valve such as a pilot operated spool valve in the form of a macro-sized valve or a microvalve.
Another type of microvalve device is a pilot operated microvalve. Typically, such a microvalve device includes a micro spool valve that is pilot operated by a microvalve of the type as described above. For example, U.S. Pat. Nos. 6,494,804; 6,540,203; 6,637,722; 6,694,998; 6,755,761; 6,845,962; and 6,994,115, the disclosures of which are incorporated herein by reference, disclose pilot operated microvalves and microvalves acting as pilot valves. One type of pilot operated microvalve is the micro spool valve. The micro spool valve typically consists of a micromachined spool disposed in a chamber formed in an intermediate layer of multilayer valve housing. Various ports through the layers of the housing provide fluid communication with the chamber. The micromachined spool is moveable in the chamber to selectively allow fluid communication though the chamber by blocking particular ports depending on the desired result. In operation, a balance of forces acting on the micromachined spool is varied to move the micromachined spool into a desired position. Typically, the balance of forces includes forces generated by differential pressure acting on the spool, which differential pressure is controlled by a pilot valve.
Microvalve devices have application in many fields for controlling the flow of fluids in systems such as hydraulic, pneumatic, and refrigerant systems, including the Heating, Ventilation, and Air Conditioning (HVAC) field. HVAC systems may include, without limitation, such systems as refrigeration systems, air conditioning systems, air handling systems, chilled water systems, etc. Many HVAC systems, including air conditioning and refrigeration systems operate by circulating a refrigerant fluid between a first heat exchanger (an evaporator), where the refrigerant fluid gains heat energy, and a second heat exchanger (a condenser), where heat energy in the refrigerant fluid is rejected from the HVAC system.
One type of HVAC system is the heat pump system (which may also be called a “heat pump type refrigeration cycle apparatus”), which provides the ability to reverse flow of refrigerant through portions of the HVAC system. Conventionally, in the heat pump type refrigeration cycle apparatus, an expansion valve is interposed between an outdoor heat exchanger and an indoor heat exchanger. In a cooling mode, a refrigerant from the outdoor heat exchanger is expanded by the expansion valve and guided to the indoor heat exchanger. In a heating mode, the refrigerant from the indoor heat exchanger is expanded by the expansion valve and guided to the outdoor heat exchanger. This allows the heat pump type refrigeration cycle apparatus operating in the cooling mode to act as an air conditioning system in the summer, cooling air that flows through a first heat exchanger by absorbing the heat from the air into a refrigerant pumped through the first heat exchanger. The refrigerant then flows to a second heat exchanger, where the heat gained by the refrigerant in the first heat exchanger is rejected. However, during the winter, when the heat pump type refrigeration cycle apparatus is operated in the heating mode, the flow of refrigerant between the first and second heat exchangers is reversed. Heat is absorbed into the refrigerant in the second heat exchanger, and the refrigerant flows to the first heat exchanger, where the heat is rejected from the refrigerant into the air flowing through the first heat exchanger, warming the air passing through the first heat exchanger.
In many heat pump type refrigeration cycle apparatuses, the expansion valve is provided at the outdoor heat exchanger (outdoor unit) side. In this case, the refrigerant expanded by the expansion valve flows into the indoor heat exchanger via a long pipeline. This is problematic, in that the expanded refrigerant is subject to pressure loss, and flow rate control by the single expansion valve is difficult. A similar problem exists, if the single expansion valve is provided at the indoor heat exchanger side; when flow is reversed, the expansion valve is not optimally placed for best control. Accordingly, some heat pump type refrigeration cycle apparatuses include two expansion valves, each one installed adjacent a respective one of the two heat exchangers. Only one of the two expansion valves is controlling flow at a time, depending on which one is optimally placed adjacent the appropriate heat exchanger for the current mode of operation, and the other is non-controlling. One problem that exists in such a system with two expansion valves is how to route refrigerant flow through the section of the system in which the non-controlling expansion valve is located.
One prior art method of dealing with this problem is illustrated in FIG. 1, in which a first expansion valve 10a is mounted on an outdoor unit 11, and a second expansion valve 10b is mounted on an indoor unit 12. As will be further explained below, a check valve 13 is mounted to allow flow to bypass the first expansion valve 10a when the first expansion valve 10a is the non-controlling expansion valve. Similarly, a check valve 15 is mounted to allow flow to bypass the second expansion valve 10b when the second expansion valve 10b is the non-controlling expansion valve. Further, an outdoor heat exchanger 20 is mounted on the outdoor unit 11, and an indoor heat exchanger 30 is mounted on the indoor unit 12. A flow path switching valve 40 and a compressor 50 may be mounted on the outdoor unit 11. The expansion valves 10a, 10b, the check valves 13, 15, the outdoor heat exchanger 20, the indoor heat exchanger 30, the flow path switching valve 40 and the compressor 50 are connected as shown in FIG. 1, and compose the heat pump type refrigeration cycle apparatus. Incidental components, such as an accumulator, a pressure sensor, a thermal sensor and the like, are not shown in FIG. 1.
The flow path switching valve 40 switches the flow path of the refrigeration cycle apparatus to a cooling mode or a heating mode. In the cooling mode, as indicated by a solid-line arrow in FIG. 1, the refrigerant compressed by the compressor 50 flows from the flow path switching valve 40 to the outdoor heat exchanger 20 (where the refrigerant gives off heat). Then, most or all of the refrigerant (as will be explained below) flows around the non-controlling first expansion valve 10a via the first check valve 13, and thence, via a pipeline 60 to the controlling second expansion valve 10b. Then, the refrigerant is expanded by this second expansion valve 10b and flows to the indoor heat exchanger 30 where heat is absorbed by the refrigerant, cooling the indoor space. The refrigerant then flows from the indoor heat exchanger 30 into the compressor 50 via the flow path switching valve 40. On the other hand, in the heating mode as indicated by a dashed-line arrow in FIG. 1, the refrigerant compressed by the compressor 50 flows from the flow path switching valve 40 into the indoor heat exchanger 30 (where the refrigerant gives off heat, warming the indoor space. Most or all of the refrigerant (as will be explained below) then flows around the non-controlling second expansion valve 10b via the second check valve 15, and thence, via the pipeline 60 to the first expansion valve 10a. The refrigerant is expanded by this first expansion valve 10a and then circulates to the outdoor heat exchanger 20 (where heat is absorbed into the refrigerant), the flow path switching valve 40, and the compressor 50. Accordingly, in the cooling mode, the outdoor heat exchanger 20 works as a condenser, and the indoor heat exchanger 30 works as an evaporator to cool a room interior. Further, in the heating mode, the outdoor heat exchanger 20 works as the evaporator, and the indoor heat exchanger 30 works as the condenser to heat the room interior.
When the expansion valves 10a, 10b are controlling flow, they are in a semi-closed state to control the flow rate of the refrigerant, and the entire refrigerant flowing through the pipeline 60 flows through the controlling expansion valve 10a, 10b. However, when the expansion valve 10a, 10b is non-controlling, most or all of the refrigerant flowing through the pipeline 60 bypasses the non-controlling expansion valve 10a, 10b via the associated check valve 13, 15. Only a minority (or perhaps none, depending upon the design of the expansion valve 10a, 10b) of the refrigerant flowing through the pipeline 60 will flow through a non-controlling expansion valve 10a, 10b. In some prior art designs, a first flow path exists through the expansion valve 10a, 10b when the expansion valve 10a, 10b is a non-controlling expansion valve. This first flow path passes a maximum flow rate of fluid through the expansion valve 10a, 10b in a direction opposite that in which fluid flows with the expansion valve 10a, 10b is a controlling expansion valve, which maximum flow rate through this first flow path is less than the flow rate through a second flow path through the associated check valve 13, 15 when expansion valve 10a, 10b is a non-controlling expansion valve. In other prior art designs, no flow path exists through the expansion valve 10a, 10b when the expansion valve 10a, 10b is a non-controlling expansion valve. In such case, the maximum flow rate through the non-controlling expansion valve 10a, 10b is zero, which again will be less than a second flow rate through the through the associated check valve 13, 15 when the expansion valve 10a, 10b is a non-controlling expansion valve.